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NEWPORT - Although public attention tends to focus on such temporary conditions as El Nino, a federal fisheries biologist says the real key to the rise and fall of fish stocks may lie with much larger, long-term climate cycles.

Rainfall, temperature and other conditions appear to shift in cycles of about 60 years, according to Pete Lawson, a research biologist with the National Marine Fisheries Service. "That raises all kinds of questions about how the fishing industry can plan its business cycles, given the kinds of fluctuations we'd expect to see in the resource just in the normal course of events," Lawson said.

Lawson will discuss what science knows, and is beginning to learn, about ocean climate cycles in a Jan. 8 seminar at Oregon State University's Hatfield Marine Science Center. The free, 1 p.m. seminar is part of a series for fishermen sponsored by Oregon Sea Grant, the OSU-based ocean research, education and outreach program.

The fishing industry has been urging regulatory bodies to use "better science" to back their decisions on harvest limits and other restrictions on species whose numbers appear to be in decline. One difficulty, Lawson said, is that scientists know too little about how climate affects different fish species.

Researchers are learning that climatic conditions vary over long cycles - on the order of 60 years or more. But recorded data describing those cycles goes back fewer than 150 years.

In the absence of recorded human observation, scientists turn to the natural record. For instance, trees in Arizona show growth rings going back about 1,500 years, with 60-year cycles in the trees' rate of growth. That, in turn, indicates long-term patterns of wet and dry, hot and cold.

Tree-ring data can be compared with other information - for instance, records of anchovy scale deposits in the ocean sediments off southern California - to get some idea about how fish populations fared at various points in the climate cycle.

As more data and sophisticated models are developed, scientists become better able to make educated guesses about how long-term climate conditions may affect the supply, range and survival of different fish species.

Lawson expects fishermen who attend his seminar to come with questions he cannot answer.

"In a way, it's a lot easier to make general statements about the kinds of things we can expect to happen over the next 60 years than it is to say what's going to happen with a specific stock over the next five years," he said. "I think the fishing industry has to plan for uncertainty, because we will never know everything that causes these fluctuations to occur."